iOS：如何创建核心数据库的备份副本？以及如何导出/导入该副本？

Question

我想为我的应用程序的用户提供创建核心数据数据库备份的可能性，尤其是在他切换到新设备等情况下。

我该怎么做？特别是如何重新导入该文件？我的意思是，假设他制作了数据库的备份副本，然后更改了大量内容并希望重置为之前保存的备份副本。我该怎么做？

谢谢！

Answer 1

看看这个示例应用程序，它包括制作备份、将备份复制到 iCloud 和从 iCloud 复制备份、通过电子邮件发送备份以及从电子邮件导入备份的功能。 http://ossh.com.au/design-and-technology/software-development/sample-library-style-ios-core-data-app-with-icloud-integration/

顺便说一句，使用 migratePersistentStore API 来制作/导入备份会更安全，如果您在 ICloud 之间这样做的话。另请注意，示例应用程序假定您未使用 WAL 模式，这是 iOS 7 的默认模式。WAL 模式使用多个文件，所有文件都需要备份或复制。

这里是演示示例应用程序备份和恢复功能的视频的链接。

http://ossh.com.au/design-and-technology/software-development/sample-library-style-ios-core-data-app-with-icloud-integration/sample-apps-explanations/backup-files/

以下是用于创建备份副本的方法。请注意，可以使用多个persistentStoreCoordinators 打开存储，因此在进行备份时无需关闭它。恢复它显然需要先删除现有的商店。请注意，以下两种方法几乎没有区别，只是源存储是在有或没有 iCloud 选项的情况下打开的。

    /*! Creates a backup of the ICloud store

     @return Returns YES of file was migrated or NO if not.
     */
    - (bool)backupICloudStore {
        FLOG(@"backupICloudStore called");


        // Lets use the existing PSC
        NSPersistentStoreCoordinator *migrationPSC = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];

        // Open the store
        id sourceStore = [migrationPSC addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:[self icloudStoreURL] options:[self icloudStoreOptions] error:nil];

        if (!sourceStore) {

            FLOG(@" failed to add old store");
            migrationPSC = nil;
            return FALSE;
        } else {
            FLOG(@" Successfully added store to migrate");

            NSError *error;

            FLOG(@" About to migrate the store...");
            id migrationSuccess = [migrationPSC migratePersistentStore:sourceStore toURL:[self backupStoreURL] options:[self localStoreOptions] withType:NSSQLiteStoreType error:&error];

            if (migrationSuccess) {
                FLOG(@"store successfully backed up");
                migrationPSC = nil;
                // Now reset the backup preference
                [[NSUserDefaults standardUserDefaults] setBool:NO forKey:_makeBackupPreferenceKey];
                [[NSUserDefaults standardUserDefaults] synchronize];
                return TRUE;
            }
            else {
                FLOG(@"Failed to backup store: %@, %@", error, error.userInfo);
                migrationPSC = nil;
                return FALSE;
            }

        }
        migrationPSC = nil;
        return FALSE;
    }
    /*! Creates a backup of the Local store

     @return Returns YES of file was migrated or NO if not.
     */
    - (bool)backupLocalStore {
        FLOG(@"backupLocalStore called");


        // Lets use the existing PSC
        NSPersistentStoreCoordinator *migrationPSC = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];

        // Open the store
        id sourceStore = [migrationPSC addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:[self localStoreURL] options:[self localStoreOptions] error:nil];

        if (!sourceStore) {

            FLOG(@" failed to add old store");
            migrationPSC = nil;
            return FALSE;
        } else {
            FLOG(@" Successfully added store to migrate");

            NSError *error;

            FLOG(@" About to migrate the store...");
            id migrationSuccess = [migrationPSC migratePersistentStore:sourceStore toURL:[self backupStoreURL] options:[self localStoreOptions] withType:NSSQLiteStoreType error:&error];

            if (migrationSuccess) {
                FLOG(@"store successfully backed up");
                migrationPSC = nil;
                // Now reset the backup preference
                [[NSUserDefaults standardUserDefaults] setBool:NO forKey:_makeBackupPreferenceKey];
                [[NSUserDefaults standardUserDefaults] synchronize];
                return TRUE;
            }
            else {
                FLOG(@"Failed to backup store: %@, %@", error, error.userInfo);
                migrationPSC = nil;
                return FALSE;
            }

        }
        migrationPSC = nil;
        return FALSE;
    }

/**  Sets the selected file as the current store.
 Creates a backup of the current store first.

 @param fileURL The URL for the file to use.
 */
- (BOOL)restoreFile:(NSURL *)fileURL {
    FLOG(@" called");

    // Check if we are using iCloud
    if (_isCloudEnabled) {
        FLOG(@" using iCloud store so OK to restore");
        NSURL *currentURL = [self storeURL];
        FLOG(@" currentURL is %@", currentURL);

        FLOG(@" URL to use is %@", fileURL);

        [self saveContext];

        [self backupCurrentStoreWithNoCheck];

        // Close the current store and delete it
        _persistentStoreCoordinator = nil;
        _managedObjectContext = nil;

        [self removeICloudStore];

        [self moveStoreFileToICloud:fileURL delete:NO backup:NO];


    } else {
        FLOG(@" using local store so OK to restore");
        NSURL *currentURL = [self storeURL];
        FLOG(@" currentURL is %@", currentURL);

        FLOG(@" URL to use is %@", fileURL);

        [self saveContext];

        [self backupCurrentStoreWithNoCheck];

        // Close the current store and delete it
        _persistentStoreCoordinator = nil;
        _managedObjectContext = nil;

        NSError *error = nil;
        NSFileManager *fm = [[NSFileManager alloc] init];

        // Delete the current store file
        if ([fm fileExistsAtPath:[currentURL path]]) {
            FLOG(@" target file exists");
            if (![fm removeItemAtURL:currentURL error:&error]) {
                FLOG(@" error unable to remove current store file");
                NSLog(@"Error removing item Error: %@, %@", error, error.userInfo);
                return FALSE;
            } else {
                FLOG(@" current store file removed");
            }
        }

        //
        //simply copy the file over
        BOOL copySuccess = [fm copyItemAtPath:[fileURL path]
                                       toPath:[currentURL path]
                                        error:&error];
        if (copySuccess) {
            FLOG(@" replaced current store file successfully");
            //[self postFileUpdateNotification];
        } else {
            FLOG(@"Error copying items Error: %@, %@", error, error.userInfo);
            return FALSE;
        }
    }

    // Now open the store again

    [self openPersistentStore];

    return TRUE;
}

Answer 2

无论您使用什么持久存储（二进制、SQLite 等）；它只是文件系统上的一个文件。您可以随时复制它。

如果您在 iOS 7 中使用 SQLite，请务必复制与其关联的其他文件，因为它们是随附的日志文件。如果您使用的是二进制文件，那么将只有一个文件。

如果你只是复制文件没有导入步骤，你只需将它复制回来即可恢复它。

还有更高级的设计，例如将整个数据库导出为可移植的东西，例如 JSON，但这是一个不同的主题。

更新

我使用了标准的 Xcode 核心数据模板，所以根据我刚刚检查的代码，我使用的是 SQLite。那么如何找到所有相关文件呢？或者你能用一些示例代码告诉我如何复制和插入所需的文件吗？

您使用NSFileManager 来复制文件。您可以查看 iOS 模拟器应用程序中的文档目录以查看所有文件的名称。或者您可以使用NSFileManager 扫描文档目录，找到以相同文件名开头的所有内容（例如MyData.*）并将其复制到备份目录中。

至于示例代码，没有；查看NSFileManager 的文档后，只需几行代码。

Answer 3

我在 Apple 示例 code 的帮助下创建了以下方法。这将备份核心数据文件并将其放置到您想要的路径。

斯威夫特 5

/// Backing up store type to a new and unique location
/// The method is illustrated in the following code fragment, which shows how you can use migratePersistentStore to take a back up of a store and save it from one location to another.
/// If the old store type is XML, the example also converts the store to SQLite.
/// - Parameters:
///   - path: Where you want the backup to be done, please create a new unique directory with timestamp or the guid
///   - completion: Passes error in case of error or pass nil in case of success
class func backUpCoreDataFiles(path : URL, completion : @escaping (_ error : String?) -> ())
{

    // Every time new container is a must as migratePersistentStore method will loose the reference to the container on migration
    let container = NSPersistentContainer(name : "<YourDataModelName>")
    container.loadPersistentStores
        { (storeDescription, error) in
            if let error = error
            {
                fatalError("Failed to load store: \(error)")
            }
    }
    let coordinator = container.persistentStoreCoordinator
    let store = coordinator.persistentStores[0]
    do
    {
        try coordinator.migratePersistentStore(store, to : path, options : nil, withType : NSSQLiteStoreType)
        completion(nil)
    }
    catch
    {
        completion("\(Errors.coredataBackupError)\(error.localizedDescription)")
    }
}